Paul Fronstin, an analyst at the Washington-based Employee Benefit Research Institute, and M. Christopher Roebuck, an analyst at Hunt Valley, Maryland-based RxEconomics, have published data on the effects of use of high-deductible coverage on health care spending in a new review of data for workers and dependents who were enrolled in a large U.S. manufacturer's health plan from 2009 through 2014.

Many of the plan enrollees were eligible for health savings accounts. That meant that the enrollees' annual deductibles were high enough to qualify them to contribute to HSAs, but that their annual out-of-pocket spending maximum amounts were low enough to meet HSA program requirements.

The enrollees did not necessarily have HSAs, and they did not necessarily contribute to any HSAs that they happened to have.

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The employer's plan covered about 150,000 to 200,000 people during each year included in the study sample.

In 2013, the enrollees submitted claims for an average of about $4,029 each in health care spending. When broken down by wage category, the totals ranged from $3,338 per year for the lowest-wage workers, who earned less than $50,000 per year from the manufacturer, to $4,148 for the highest-wage workers, who earned $125,000 or more.

Fronstin and Roebuck found that using the HSA-eligible plan had a dramatic effect on the enrollees in the lowest-wage category.

Typical enrollees in that wage category spent an average of about $619 on prescription drugs in 2013.

Over the period from 2009 through 2014, using an HSA-eligible plan cut those enrollees' prescription drug claims by an average of about $435 per year. The spending cut amounted to 70 percent of 2013 drug spending.

Enrollees in the $125,000-and-over category spent an average of $998 on drugs in 2013. Over the period from 2009 through 2014, use of an HSA-eligible plan reduced their drug spending by an average of $244 per year. That's equal to about 24 percent of the 2013 spending total.

HSAs had a modest effect on most other types of health care spending.

One exception was spending on emergency room care by the lowest-wage workers, and those workers' dependents.

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Those workers' families spent an average of only $176 on emergency room care in 2013, but use of an HSA-eligible plan correlated with $82 in extra annual emergency room spending per person.

That means that, even though the dollar value of the increase in ER spending was low, use of HSA-eligible coverage correlated with a 50 percent increase in ER spending.

Fronstin and Roebuck say that effect appears to be temporary, but that they see signs in their data that workers with HSA-eligible coverage need more information about the preventive services they can get with no out-of-pocket cost, before they meet the plan deductible.